Professional tradesmen are often quite familiar with most appliances because they install them on a regular basis. Looking at the manual was usually something they did when the item was brand new on the market, and they understood what was needed. Memory is often what they rely upon to get the work done in a timely fashion, and it does cut down on the time it takes for installation. For those doing their own appliance installation, it can pay off handsomely to read the manual first.
Going through the manual could seem like a waste of time, but it could help avoid the cost of hiring a professional when the job becomes overwhelming. Many appliances today have computer chips embedded in them, and that alone can stop the project. Knowing exactly what has to be done beforehand can let a person know whether or not they should call in help. Getting a project half done and finding out it is wrong can cost much more than the entire installation by a professional.
Those few leftover parts may be part of a necessary function, but finding that out when the appliance does not work can be a costly mistake. Professional installers charge for the time it takes to do the work, and figuring out where those leftover parts should have been installed takes time. They will then need to uninstall the appliance, add the parts and finish the installation. All of this can cost more than hiring them to do the entire job.
There are times when a person doing an installation on their own gets stuck without having leftover parts or mistakes that need to be corrected. Recognizing that they are unable to finish the work is when they should immediately call in a professional. The ability to explain clearly what has been done and where they stopped in the process can save time and money, and it may even earn them the respect of a person who does that work for a living.